Hydraulic fluids



United States Patent 3,324,035 HYDRAULIC FLUIDS Robert J. Nankee,Midland, Joseph E. Schrerns, Saginaw, and Ernest L. Caldwell, Midland,Mich., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware No Drawing. Filed Mar. 11, 1964, Ser. No.351,228 Claims. (Cl. 252--73) This invention relates to a new super highboiling hydraulic fluid having very low pour point and other desirableproperties.

Hydraulic fluids, for example automobile brake fluids, are subject toincreasingly stringent requirements in their functional properties. Forexample, there is a constant demand for fluids having higher boilingpoints, lower pour points, greater lubricity, less corrosiveness towardthe numerous metals encountered in hydraulic systems, less rubber swelland less change of viscosity with changing temperature. Frequently achange in composition which improves one or more of these or otheressential properties is of little or no value because of a harmfuleffect on some other property. Thus, most attempts to produce fluidshaving higher boiling points have resulted in fluids having higher pourpoint, rubber swell and/or lowtemperature viscosity.

According to the present invention, hydraulic fluids are provided whichhave exceptionally high boiling point and at the same time have very lowpour points, low rubber swell and low viscosity at -40 F. In these andall other properties, when compounded with conventional antioxidants andcorrosion inhibitors, they easily pass the SAE brake fluidspecifications 70R1 and 70R3. These consist entirely, or at least inmajor part, of one or more compounds having the formula wherein R is aprimary lower alkyl radical, i.e., one containing 1 to 4 carbon atoms,m, n and p are integers from 2 to 4, at least one of them being 2, andx, y and z are integers, x and y being 1 to 5 and 2 being 0 to 3, thesum of x, y and 2 being 4 to 8, at least 50% of the oxyalkylene groupsbeing oxyethylene groups.

US. Patent 3,062,747 discloses lower alkyl monoethers of heteric(random) copolymers of ethylene and propylene oxides containing up toabout 5 oxyalkylene units. While these are useful as brake fluidssuitable for ordinary requirements, they cannot meet heavy dutyrequirements such as for pour points below -60 F., viscosity at 40 P.not more than 1800 cstks., and

boiling points of the order of 550 F. or more. This difference incritical properties apparently stems from the.

differences in the structure of the polyoxyalkylene chains of the twoproducts; i.e., disordered vs. ordered (heteric vs. block) copolymers.

The compounds of the above formula can be conveniently made by the wellknown methods for making polyoxyalkylene glycol ethers, as taught, forexample, in the above cited patent or in US. Patent 2,174,761 or2,425,755. In general, a suitable procedure consists of condensing alower alkanol with an alkylene oxide by use of an oxyalkylation catalystuntil 1 to 5 moles of oxide have reacted, then continuing theoxyalkylation with a second alkylene oxide until 1 to 5 moles of thisoxide have reacted and, optionally, continuing the oxyalkylation with analkylene oxide which is different from the second oxide, though it maybe the same as the first, until up to 3 moles thereof have reacted. Theproduct, after devolatilization, is ready for use.

3,324,035 Patented June 6, 1967 "numbers of oxaylkylene units. Thus, forexample, when 3 moles of alkylene oxide are condensed with 1 mole ofalkanol, the product consists of a mixture of ethers containing anaverage of 3 oxyalkylene groups per molecule but some of the individualcomponents contain more than 3 and some contain less than 3 oxyalkylenegroups. Such mixtures of closely related compounds having similarproperties are generally useful for the same purposes as the individualcompounds and generally no attempt is made to separate them. Thecompounds of the present invention follow this general rule in that theyare usually produced as cogeneric mixtures which can only be describedin terms of their average composition. However, since they are ofrelatively low molecular weight, it is possible to separate them byfractional distillation in vacuum stills. The formulas used herein areintended to represent not only the specific, individual compound but thecogeneric mixture having the indicated average composition.

In making the compounds of the invention it has been found advantageousin certain cases to fractionate, at least partially, the intermediateether produced by condensing the first alkylene oxide, C H O, with thealkanol, ROH. Thus, if, for instance, a final product is desired havingthe above formula wherein x is 3, it might be made from an intermediatehaving the formula R(OC H OH. This intermediate would ordinarily be madeby condensing 3 moles of the appropriate alkylene oxide with the alkanolROH. It may then be used as a cogeneric mixture or it may befractionated to remove the fraction containing the diglycol ether (x=2).The residue may then be used as such or it maybe further fractionated toisolate the specific material wherein x=3, thus eliminating the smallproportion of highers that is normally present wherein x=4 or more. Suchfractionation can also be carried out after the condensation of thesecond and/or third alkylene oxide, though it becomes increasinglydifiicult as themolecular weight of the material increases. Ordinarilysuch later fractionation is limited to a devolatilization step to removetraces of unreacted oxide, glycol and/or low-boiling ethers.

The preparation of the compounds and practice of the invention isillustrated by the following examples.

EXAMPLES 1-9 General procedure with nitrogen and heated to 110 C. Thefirst alkylene oxide was then fed in until the calculated amount wasreached. Heating and stirring were then continued until substantiallyall of the oxide had reacted, as indicated by the pressure.

The product was then devolatilized in vacuum to remove all compoundsboiling below the desired ether.

In the second stage, the product of the above stage was furthercondensed with a second alkylene oxide and then, in some instances, witha further portion of the first alkylene oxide. The final product wasneutralized with phosphoric acid or fatty acid, devolatilized andfiltered. Products produced in this way are shown in the followingtable.

4 -40, the viscosity of the liquid being 1130 cstks. It is thus apparentthat unexpectedly valuable fluids are obtained by blending up to about45% by volume of R m x n y D Z No. 9 with No. 2, the optimum being atabout 2535%.

5 Example 10 in Table II illustrates one such blend. 3 g 93 g 8-3 Thecompounds of the invention are not only com- 2 3 2 patible with eachother in brake fluid blends but are also i g 2 8 compatible with anduseful in combination with other 2 3 1 III: 0 conventional non-aqueousbrake fluid components, such 3 3 5 g 10 as the alkylene glycols,diglycols and polyglycols and the 2 4:4 0' 0 simple ethers and esters ofsuch glycols. In general, the brake fluids comprising the products ofthe invention The above Products, Separately and in Various combiarecompatible with the conventional brake fluid additives nations, weretested as brake fl id according to SAE such as corros1on inhibitors,antioxidants, etc. Suitable S ifi ti 70 1 and 70R3 Results with the morecorrosion inhibitors include the borate salts and esters, critical testsare shown in Table II. All materials, whe ni te al s,mercaptobenzothiazole, etc. Antioxid nts compounded with conventionalcorrosion inhibitors and lncludfi bls phenol A, dlalkylphenols andafomatlc amlnesantioxidants, readily passed all the other tests in theWe clalmi above specifications. The materials tested in Examples In amethod PP Y P S 3 hydfflullc 1-9 of Table II were those described in thecorrespondbrake through a Y P bfifke fluid, "E Improvement ing Examples1-9 of Table I. It may be noted th t hil wherein the brake fluidconsists essentially of at least the product of Example 9, alone, is nota part of the one Compound havlng the formula present invention, it isparticularly useful for blending R(OC H2 H with the other products ofthe invention to produce brake m on n y 2p Z fluids, as will be shownhereinafter. wherein R 1s a primary lower alkyl radical, m, n and 7TABLE II.IROPERTIES OF PRODUCTS Viscosity, Ostks. Pour Boiling RubberEx. No. Viscosity Point, Point, Swell,

Index F. Percent -40 F. 100 F. 210 F.

1, 525 s. 20 2.10 59 -100 520 2. 5 1, 510 8.26 2.14 55 100 560 2. 4 2,040 0. 2. 42 83 -7s 503 4. 2 985 7. 77 2.10 57 -100 572 8.1 2, 500 9. 002. 09 97 590 3. 9 770 5. 01 1. 91 -100 552 9. 4 3,000+ 10. 2.05 84 -05538 5.0 1, 409 8. 28 2.13 51 -100 554 2. 5 send 8. 00 2. 22 80 35 582 0.3 1,320 8.20 2. 15 51 -100 551 3. 5 3 1,800 3 5s 4 375 0. 5-4.0

1 Blend of 67.5% by volume of No. 2 and 82.5% of N0. 9. 2 SAE 70R3minimum specifications.

3 Maximum.

l Minimum.

The data in Table II shows that although many of the products of thepresent invention qualify in all essential respects as single-componentbrake fluids (when inhibited with suitable conventional antioxidants andcorrosion inhibitors), others are deficient in one or more respects.Thus No. 3, 5 and 7 are too viscous at 40 While No. 4 and 6 swell rubberexcessively. These, however, as well as No. 9, are extremely useful formaking blends of two or more components, thus improving their deficientproperties and taking advantage of their outstanding valuableproperties, such as high boiling points and/or low pour points. Inaddition, unexpected improvements in viscosity were observed in suchblends. Thus, for example, when fluid No. 2 was blended with increasingamounts of No. 9 it was found that the pour point remained below theacetone-Dry Ice limit (about 100 F.) until about 32-35% by volume of No.9 was reached. The pour point then began to rise and at 40% it was -70F. and at 50% was 53 F. At the same time the 40 F. viscosity dropped ina linear fashion, being 1380 at 25% and 1280 at 40%. This trendcontinued to 60%, at which point the blend froze after 2 hours at areintegers from 2 to 4, at least one of them being 2, n being differentfrom both in and p and x, y and z are integers, x and y being 1 to 5 andz being 0 to 3, the sum of x, y and z being 4 to 8, at least 50% of theoxyalkylene groups being oxyethylene groups.

2. A method as defined in claim 1 wherein m and p are each 2 and n is 3.

3. A method as defined in claim 1 wherein x is 3 to 4, y is 1 to 3, z is1 to 2 and 20+y;+z=5 to 7.

4. A method as defined in claim 2 wherein x is 3 to 4, yis1to2andzis 1.

5. A method as defined in claim 4 wherein R is methyl.

References Cited UNITED STATES PATENTS 3,030,426 4/1962 Moseley et al.260615 3,062,747 11/1962 Fife et al. 252-73 LEON D. ROSDOL, PrimaryExaminer.

R. D. LOVERING, S. D, SCHWARTZ,

Assistant Examiners.

1. IN A METHOD FOR APPLYING PRESSURE TO A HYDRAULIC BRAKE THROUGH AHYDRAULIC BRAKE FLUID, THE IMPROVEMENT WHEREIN THE BRAKE FLUID CONSISTSESSENTIALLY OF AT LEAST ONE COMPOUND HAVING THE FORMULA